#!/usr/bin/env python
# coding=utf-8


class Stack:
    def __init__(self):
        self.values = []

    def push(self, value):
        self.values.append(value)

    def pop(self):
        return self.values.pop()

    def is_empty(self):
        return self.size() == 0

    def size(self):
        return len(self.values)

    def peak(self):
        return self.values[self.size() - 1]


